visitor_id = window["optimizely"].get("visitor_id");

Parameter and Type	Child Attribute	Description
visitor_id string	N/A	The argument indicating to get visitor_id information. Required.

Parameter and Type	Child Attribute	Description
VisitorIdsObject	N/A	The visitor ID object contains the visitor ID assigned by Optimizely Web Experimentation.
randomId string	Child attribute of type `VisitorIdsObject`.	A randomly generated user ID for the current visitor, which is used by Web Experimentation for calculating your results.

visitor_id = window["optimizely"].get("visitor_id");

{
  "randomId": "oeu1470101898133r0.04568111757824678"
}